Any guidance on selecting these? Tips on use welcomed as well. Many sizes and they range from not-cheap to expensive, so any advice on where to start?

The need comes up with some regularity whether it's a ratty old gun am rehabbing or making a new screw. And no, won't touch one of my good firearms until have practiced on plenty of beaters.

You will need a roller guide to keep the file in position when making new screws. Brownells sells one: http://www.brownells.com/gunsmith-t...sories/screw-slot-fixture-prod18694.aspx Freehand cutting a new slot is not going to work unless you have the skills of a watchmaker and even they use file guides. You cannot buy too high quality for such precision work. The best files are made in Europe and are expensive.

If you have a drill press, this might be of some interest:
http://www.shootingtimes.com/gunsmithing/gunsmithing_a_better_way_to_slot_screws_011211/

RAN

RAN